Kudzu Bug Q&A

by Xing Ping Hu, Extension Entomologist, Auburn University

What is a Kudzu bug?
The Kudzu bug is a small yellowish green lady-beetle-like insect. However, they are not a beetle, but a true stink bug with sucking mouths that sip the juice from plants.

They like to aggregate in clusters and release a very strong, foul odor that you can smell several feet away.

Kudzu bugs are also called lablab bugs, bean bugs, globular stink bugs, and bean plataspids.

Are they a new pest and where did they come from?
Yes, the Kudzu bug is a new pest for us in the United States. Many new people are being introduced to it every day. We will all have to learn the best ways to deal with it.

The Kudzu bug is native to Asia. Genetic markers indicate this bug was likely introduced from Japan.

When did they get here and how widely spread are they now?
It was first reported in Georgia in 2009 and spread to Alabama in October 2010. Since then, it has been spreading like wildfire. By the end of June, it has been confirmed in more than 430 counties across 9 Southern Region States. They are in all but 53 counties in Alabama right now.

How do they spread so rapidly?
Many factors aid in their fast dispersal:

• Hitchhiking on vehicles, airplanes, shipments of products and equipment, and even humans
• They are strong flyers themselves, capable of flying at least a couple of miles
• They are attracted to white and lightly-colored surfaces
• Propensity to migrate
• Diverse and flexible life history and rapid population growth rate
• Availability of primary hosts – kudzu plants and soybean crops
• Most interestingly, the new finding in my lab shows a majority of the adult females become fertilized before overwintering. A single pregnant female can lay egg masses in a new location without the presence of male.

What plants do they infest?
Kudzu bugs are leguminous plant feeders. Their primary host is kudzu plants; that is how they got their name. Of the other leguminous crops, they prefer soybeans to vegetable beans and wisteria vine.

However, they must feed on kudzu or soybeans to be able to reproduce. It is common to see them aggregate and feed on non-legume plants in early spring and late fall when leguminous plants are not available.

If they have been in AL since 2010, why the sudden population outbreak in soybean crops this year?
During the first year of invasion, the population was basically limited to kudzu patches. However, because of the exponential growth, overcrowding populations started to move into soybean fields in 2012 and reached peak outbreak this year.

What is the pest status of kudzu bugs?
They were first considered a nuisance pest in residential areas, but are posing much greater threat than previously thought. In Asian countries, it is a serious pest of soybean and vegetable beans. Here in the United States, besides yield loss of soybeans, it poses threats to international trade of agricultural products to Central America, and is an urban nuisance.

What damages do they cause in soybean crops?
They are slow feeders, sucking plant juice and gradually drawing down a plant’s vigor. They do not eat holes in leaves and do not take bites from pods or seed.

When do kudzu bugs move onto soybean plants and how long they stay in soybean field?
It depends on whether you have early, middle, or later soybean crops and the climate. In 2013, we observed adults of an overwinter generation move to lay egg masses on early-planted soybean crops when they are about 1 ft tall. Nymphs appeared in late May and by the middle of June, nymph population had peaked across the entire soybean field. This was also the optimal time for control treatment.

You will see Kudzu bugs in the field until the soybean plants become unsuitable (not enough juice). Last year’s research showed that Kudzu bug population was greater in early-planted soybeans rather than later-planted soybeans. We are monitoring Kudzu bug population dynamics this year.

Kudzu Bug Management and Control in Alabama Soybeans

Ron Smith, Extension Entomologist, Auburn University

The Kudzu bug has become a major economic pest of Alabama soybeans in certain fields throughout the state in recent weeks. Populations as high as 50 or more adult bugs per plant were observed in early June. Some of these fields now have 200 or more immature bugs per plant (late June). Calls are being received from growers and field men in recent days from all over the state.

Kudzu bugs are most highly attracted to early planted (April and early May) soybeans. Beans planted later, for example following wheat harvest, are much less attractive.

The primary question asked are when should soybeans be treated and what insecticide should be applied. The second part of the question is the easiest to answer. Most pyrethroid insecticides do a good job of controlling Kudzu bugs. Working thresholds have been previously established by entomologists in Georgia, North Carolina and South Carolina. For pre-flower vegetative beans a treatment threshold of five adults per plant is suggested. After flower, a threshold of one immature per sweep, with a sweep net, is recommended. As an alternative to sweep-net sampling, visual inspections of insect density lower in the canopy will suffice.  If immature kudzu bugs are easily and repeatedly found on the leaf petioles and/or main stems, treatment is likely warranted. However, these threshold guides may be modified slightly based on the number of egg masses that are continuing to hatch.

Kudzu bugs have two generations per season on soybeans. Adults move from Kudzu to early planted soybeans in the spring, deposit egg masses and eventually die. The immatures then hatch and eventually become adults after about six weeks and begin to deposit eggs for the next generation.

A limited number of Kudzu bugs may appear in beans season long. The most efficient and economic use of insecticides occurs when an application is made when the majority of the population in each generation is in the immature stage. Some fields have already exceeded treatment threshold and will likely require two or more sprays during the 2013 season. Fields with lower populations may be able to wait until mid-July or later for a treatment. Only one application may be needed in these fields during the 2013 season. 

Applications made when a high number of unhatched egg masses are present may have to be repeated within one to two weeks. Our goal should be to strategically time these insecticide applications for maximum effectiveness. Treating soybeans repeatedly at close intervals has not resulted in yield increases over fewer well timed applications. The key point is for growers and field men to focus on the peaks of immature Kudzu bugs as we move through the 2013 season.

There will be no way to economically prevent yield losses to Kudzu bugs and minimize inputs without monitoring or scouting soybeans weekly just as we have done in other row crops for decades. Kudzu bugs are not the end of the world for soybean production in Alabama but they do create a new day. Pictures of adult and immatures are available on Ron Smith’s blog http://alabama-insects.blogspot.com/. Basic Kudzu bug information can be found at http://www.clemson.edu/extension/Kudzubugs/index.html. Updates on the Kudzu bug status will be posted on the www.alabamacrops.com website. The Extension Soybean IPM guide has recommendations for Kudzu bugs on page six http://www.aces.edu/pubs/docs/I/IPM-0413/IPM-0413.pdf. Also, there is a podcast now available here http://agfax.com/2013/07/01/first-time-with-kudzu-bugs-listen-up/.

Adults

Egg Mass

New Release Information on Kudzu Bug by Tim Reed

STATUS OF THE DISTRIBUTION OF KUDZU BUG IN ALABAMA

The kudzu bug has been “officially” reported to occur in 53 of Alabama’s 67 counties as of June 27. Last year in the first week of June this invasive species had been reported in 15 counties. It is quite likely that this insect is now present in all Alabama counties. Several counties have reported significant populations of kudzu bugs infesting soybeans during June in Alabama in 2013 and numerous fields have been sprayed. 

LIFE CYCLE AND HOSTS OF THE KUDZU BUG

The time required for the kudzu bug to develop from an egg to the adult stage is 6 to 8 weeks. The egg hatches in about 5 days. The kudzu bug has been found on many plants but presently the only host plants on which it is known to reproduce are kudzu, soybean and wisteria.

ECONOMIC THRESHOLDS FOR KUDZU BUG ON SOYBEAN

Thresholds for kudzu bugs infesting soybeans continue to evolve as more information is gained from research efforts. Southeastern entomologists are currently recommending that growers consider using the following thresholds when making kudzu bug treatment decisions: 5 bugs per seedling, until plants are one foot tall. Then, the threshold will change to 10 bugs per plant for plants from 1-2 feet tall. The established threshold of one nymph per sweep  should be used for plants above 2 feet tall. Plants should be sampled at least 50 feet from the edge of the field.

The reason for this is that the adults have an extended migration period (6-8 weeks) and colonize field edges first. If you sample the edges, chances are you will make a spray decision too soon before the migration is over.

WHICH CHEMICALS ARE EFFECTIVE IN CONTROLLING KUDZU BUG IN SOYBEANS

Multiple classes of insecticides have shown activity on kudzu bugs. Insecticide treatments containing bifenthrin, cyhalothrin, zetacypermethrin, carbaryl, or acephate provided greater than 80 percent control 2-5 days after treatment in insecticide efficacy trials conducted in Georgia and South Carolina. Insecticides do not prevent eggs from hatching. Growers actively treating kudzu bugs with broad spectrum insecticides should consider using a preventive application of Dimilin (2 oz/acre rate) at the R2/R3 growth stage for control of velvetbean caterpillars and green cloverworms in July, especially in central and south Alabama which historically have had higher populations of velvetbean caterpillars than north Alabama.

EFFECT OF PLANTING DATE ON KUDZU BUG POPULATIONS IN SOYBEANS

Studies in Georgia and South Carolina have shown that kudzu bug populations are higher on earlier planted soybeans than on later-planted beans.

Tim Reed, Extension Entomologist, Auburn University

Insect and Crop Update for the Week of June 23

After going weeks with light to moderate thrips pressure, damage was heavy on 4-7 leaf cotton in early June, especially in SW Alabama.

Cotton was growing rapidly but thrips damage on true leaves was showing heavy damage from about the 4^th to 7^th true leaf. (Peanuts also were taking heavy damage during this same period.)

The thrips window is over now and we need to shift our focus to spider mites, aphids and the plant bug complex which includes tarnished plant bugs, fleahoppers and an occasional clouded plant bug.

Mites are primarily found in the TN Valley region of North Alabama and some treatments were being applied last week.

I noticed the first aphids on April planted cotton in central Alabama last Friday (June 21).

Plant bug numbers (adults) were down last week but nymphs are beginning to appear in our earliest planted cotton (mid-April). I would suggest using a sweep net to sample adults for the next 2-3 weeks, depending on the age of the cotton. As we approach first bloom I would switch to a drop cloth and concentrate on the presence of immature plant bugs.

Also, field men should now be looking at pinhead square set. Fields surveyed on June 21 were setting about 90% of the fruit. However, some plants had up to 30% square loss at that point. I believe you will find that migrating adult tarnished plant bugs will seek out the earliest planted and most lush cotton fields. My thought is that this cotton provides the best shade from the 95 degree temperatures, and is the best host for plant bugs.

While looking for pinhead square set I noticed a number of white eggs, likely tobacco budworms. They would not be a concern now, but in the old days it would have created a real predicament. Spraying for plant bugs during a budworm moth flight would have been expensive and also put the grower on a treatment treadmill for the remainder of the season. Sometimes we forget how well we have it compared to the pre-Bollgard years.

On another insect – a few stink bugs are already present in cotton. Normally we do not worry about stink bugs until about the third week of bloom, when we have bolls that are 10-12 days old. However, when stink bugs are present at bloom they will attack thumb sized bolls as soon as the bloom tag sheds. Any feeding to bolls this size will cause the boll to abort. Therefore, fieldmen need to be alert for adult stink bugs in early bloom cotton as they monitor for plant bugs with a sweepnet. Stink bugs will not damage squares or blooms but will seek out these first small bolls.

Since some of our corn was planted later than desired, stink bugs will likely remain with that host until the post roasting ear stage when the kernels become hard. At that time we may have a large movement into other crops such as cotton, soybeans and peanuts.

One word about Kudzu bugs on soybeans. Numbers of adults are out of site on many of our April planted beans. In fact, adult numbers are beginning to decrease in some fields now but numerous immatures are present, which is the trigger we use to treat the field. Fieldmen who have not experienced this insect may overlook these immatures when they are small. They will be a clear to greenish color and very small after hatching.

Insect Update on Cotton and Soybeans

As of 8:45 am Monday, June 10, all is quiet on the insect front. Rainfall during the past week has given cotton a growth spurt. Youngest cotton is 3 to 5 true leaves and overall has little thrips injury. Older cotton is at the 5 to 9 true leaf stage. Many fields are between the thrips injury stage and the stage where we begin to focus on plant bugs. This window is about 7 to 10 days long. Mid April planted cotton already has 2-3 pinhead or larger squares and should be scouted for adult plant bugs. No aphids or spider mites have been reported.

We will be conducting scouting schools in Autaugaville (central AL) and Headland (Wiregrass area of SE AL) this week. In addition to cotton and soybean insects (Kudzu bugs) we will also have presentations on cotton disease and resistant weed management.

Kudzu bug adults are attacking early planted soybeans in the Prattville, Tallassee and Auburn areas. At present our treatment threshold is 5 adults per plant.

Updates for Week of May 26th

Kudzu Bug adults depositing eggs in April planted soybeans in Barbour Co. (Eufala) on 5/28/13. Will wait for hatch to assess treatment needs.

Low level of cotton fleahoppers infesting 6-7 true leaf cotton at Prattville, AL.

Some controls still going out for adult grasshoppers in Central, AL. Stand loss detected from GH feeding on stems at or above soil line.

Mid May or later planted cotton with seed treatments should not need foliar thrips spray due to rapid growth of the plants.

Update for the Week of August 12

Last week was rather quiet insect wise on cotton. Many areas received thunderstorms throughout the past 7 days. The comments that I will make today are based on observations made in the field from several different areas of the state last week.

The first point is when to back off of stink bug controls. Our early April cotton is beyond the eighth or ninth week of bloom with few to no 10-12 day old bolls remaining. In fact, my test plots of PHY 375 planted April 9 had several open bolls per plant early last week. Even with cotton that still has a few 10-12 day old bolls remaining, stink bug numbers are so low in most fields that a stink bug threshold could never be reached. I would not be concerned at all with 10-20% internal damage as cotton is maturing out and beginning to open. For those who would be spraying with ground equipment, and that would consist of the majority of growers in Alabama, a ground rig going through mature cotton would destroy far more good bolls than the few smaller bolls near the top of the plant that stink bugs might injure.

Spider mites populations held steady last week but did not seem to increase, likely due to the frequent thunderstorm occurrence. I would just keep an eye on them and delay treatment decision as long as the current weather pattern holds.

One of the heaviest tobacco budworm flights seen in several years has been ongoing in the southern counties. Moths, eggs, and small larvae have occurred in high numbers from Dothan in the southeast to Fairhope in the southwest. This will have no impact on cotton with Bollgard or WideStrike technology. However, conventional varieties are a different story. I was in research plots of conventional cotton with no insect technology at Fairhope, AL on August 7 and found 32% worm square damage with 9% of the squares containing live larvae. Who says the technology has less value than it once did? In the old days, what would we do under this level of pressure, with thunderstorms occurring every afternoon?

Growers that may be impacted by this budworm pressure are soybean and peanut producers. If these crops are infested with budworms then the newer chemistry will be required because pyrethroids would not perform at all.

Chemical choices would be, in alphabetical order: Belt, Steward, or Tracer and possibly Lannate. Some might include Intrepid with this group but I do not know how effective it would be on budworms. Peanut growers should monitor their fields closely for the next 7 to 10 days for budworm numbers. New growers applying a fungicide to soybeans should not automatically add a pyrethroid for insurance purposes. If an insecticide is added in a preventative mode, I would suggest Dimilin at 2 oz. for future foliage feeders.

One other soybean pest that I will mention in closing is soybean loopers. Most soybean fields have a few green cloverworms or an occasional looper. However, one field in Baldwin County was observed last week with about 10 loopers per foot with about 10-15% foliage loss already. Therefore, all fields are not alike and must be scouted to stay on top of the soybean insects.

Soybean Insect Pest Update

Fall armyworms have been reported infesting pastures across Alabama and last week this pest was found feeding on soybeans in Lawrence County in the Town Creek area. These fall armyworms appeared to have moved from a bermudagrass pasture and crossed a wooded area to reach the soybeans. The caterpillars were feeding on the soybean foliage in the portion of the soybean field adjacent to the woods. Since this report from last week, fall armyworms and yellow striped armyworms have been found in many soybean fields in North Alabama at densities as high as 3 to 4 per 15 sweeps. Since theses armyworms have been found across the R2 to R6 soybeans, it is likely that these worms were derived from eggs deposited in the fields by moths. Only a very limited number of soybean fields have been treated strictly for foliage feeders in Alabama thus far---but numbers of green clover worms are increasing in north Alabama and velvetbean caterpillar numbers are increasing in south Alabama as far north as Monroe county. The economic threshold for foliage feeding caterpillars from pod set to maturity is as follows: Prevent greater than 20-percent leaf  loss. Treat prior to 20-percent leaf loss when five to eight foliage feeding caterpillars (soybean loopers, armyworms, green clover worms, velvetbean caterpillars)  0.25 inch long or longer, are present per foot of row.

Treat when you catch an average of 1.5 foliage feeding worms per sweep. Soybean loopers are harder to dislodge with a sweep net and each looper should be counted twice. Each larva eats a high percentage of the total amount of foliage it consumes during the last 4 to 5 days of the larval cycle. If disease is present in the population growers may wish to delay application  for 2 to 3 days, especially if larvae are less than a half inch long and populations are not much above the minimal threshold. Both fungal and viral disease can wipe out a caterpillar infestation within a week under the right conditions. Podworm and stink bug numbers have been below threshold levels thus far in the vast majority of soybean fields.  However soybeans planted behind wheat could see increasing populations of these two pests as we enter the pod-fill stage.  Three-cornered alfalfa hopper (3CAH) numbers are variable (usually less than 2 per sweep) but numbers in most untreated fields are increasing.  Some growers who applied a fungicide to their soybeans have also included an insecticide to reduce 3CAH numbers.  As soybeans mature we will see more fields with multiple insect pest species present.  At times there will be 2 or more species at densities which are just below treatment threshold levels. It can be difficult to make a treatment decision in this situation.  If you need assistance in making a soybean treatment decision you can call me at 256-627-3450.

By: Tim Reed

Kudzu Bug Found Infesting Alabama Soybeans

The kudzu bug was detected this week in 2 soybean fields in Cherokee county which borders on Georgia where the pest was first detected in the Athens/Atlanta area in 2009. The pest has spread rapidly since it was first detected and now has been found in 7 SE states. The kudzu bug had been found previously on kudzu in 25 Alabama counties but this is the first report on soybeans. Economic yield losses by soybeans due to kudzu bug feeding have been reported in Georgia. (The following information was taken from the 2012 Georgia Soybean Production Guide)  Adult kudzu bugs are oval shaped,  about ¼ inch in diameter, and greenish brown in color. Eggs are laid in double-rowed batches of 35-50 eggs and are white in color. Nymphs are also oval shaped and are light green to brown in color and have numerous setae/hairs. Both adults and nymphs are most commonly seen on plant stems using their sucking mouthparts  to feed on plant sap. The effects of kudzu bug feeding on soybeans is similar to drought. Excessive feeding weakens and stresses the plant which can result in fewer pods per plant, fewer seeds per pod, and reduced  seed size.  Overwintering adults survive under pine bark and ground debris . Key reproductive hosts of kudzu bug include kudzu, wisteria , clover and soybeans. Adults begin laying eggs on kudzu shoots in  mid-April and continue laying eggs on kudzu for several weeks. Time required to reach the adult stage is about 6-8 weeks. These new adults then disperse to soybeans and other reproductive hosts beginning in mid-June and continuing thru mid-July. Soybeans become attractive to kudzu bug adults when plants are 8-10 inches tall. Early planted soybeans appear to be at greater risk for kudzu bug infestation compared with later planted soybeans. Adults will begin laying eggs on the underside of soybean leaves and a generation requiring about 6 weeks will be completed on soybeans. Initial field invasions tend to be more concentrated on field margins but will eventually spread throughout the field. In many situations we will begin to see immature kudzu bugs in soybeans at about the R2-R3 stage. Kudzu bugs can be scouted using a 15-inch diameter sweep net. Kudzu bug populations can be extremely high. Georgia entomologists are suggesting a threshold of one immature kudzu bug per sweep. This suggested threshold is based on 2011 field trials where a single properly timed insecticide application preserved soybean yield. If insecticides are applied when adults are still actively migrating from kudzu to soybeans (late June and early-mid July); additional applications may be needed. Research is ongoing to verify and refine management and treatment thresholds for kudzu bugs in soybean. Multiple classes of insecticides have shown activity on kudzu bugs. Insecticide treatments containing bifenthrin, cyhalothrin, zeta-cypermethrin, carbaryl, or acephate provided greater than 80 percent control 2-5 days after treatment.

Current Insects in Cotton at Economic Levels

Today I would like to discuss three insects that are occurring in cotton at economic levels in certain fields. Two of these insects are actually impacting other crops, particularly soybeans and peanuts, as well.

Adult tarnished plant bugs (TPB’s) are being reported at moderate to high levels in some fields statewide. More findings are reported each day and there are likely many fields where they are present but have not been observed yet. At this point, no one has reported high pinhead square loss. This square loss is what we like to base our treatment decisions on. However, based on past experiences, once the adult TPB’s are present it is just a matter of time until some level of square loss is detected. These are all migratory adults that have moved into cotton from wild hosts. They will feed on pinhead squares, which cause abortion, and also deposit eggs in the plant stems. These eggs will hatch in two plus weeks into an immature field generation. The longer the period that adults are allowed to roam in fields, the longer the period of hatching immatures will be in coming weeks. Knowing this, growers can make their own decision as to when controls should be applied.

The second insect I will mention is the tobacco budworm (TBW). An extended flight of budworms has been ongoing in various areas for about two weeks already. This is of no significance to 98% of the states acreage that is planted to Bollgard II or WideStrike varieties. However, this makes a tricky situation in conventional cotton that may need plant bug sprays during this TBW period. This TBW flight is also impacting later planted peanuts that have a limited amount of vegetative growth. Budworm moths seem to be attracted to peanuts with a vegetative width of 3-4 inches. Earlier peanuts that have six of more inch vegetative width do not appear to have as many budworms present. We collected about 250 quarter inch budworms yesterday at Headland, Alabama on about 600 row feet. This was not what I would consider an economic or treatable level. However, up to four budworms per row foot have been reported in some fields and controls, with the newer chemistry, have been applied.

The third insect that is causing widespread concern in cotton at present is the three-cornered alfalfa hopper (3CAH). Numerous fields in the Tennessee Valley area of northern Alabama have had damaging levels of 3CAH reported. This problem has extended as far south as Talladega County. Treatments have been applied. Soybeans are also experiencing a problem with this insect, even more so than cotton, and over a much larger geographical area. 3CAH damage is caused by the girdling of the main stem of both cotton and soybeans by both the adult and immature 3CAH. No good thresholds exist from Alabama research. Usually this problem and damage is greater on field borders but consultants have reported damage field wide in both cotton and soybeans. Treatment thresholds are difficult to develop for 3CAH, just as they are for grasshoppers. Treatments sometimes have to be made based on the risk that certain species present, and not the level of damage observed. Sweep nets are very effective in documenting the number of 3CAH per row foot.

3-Cornered Alfalfa Hoppers Attacking Seedling Soybeans

Three-cornered alfalfa hoppers (3CAH’s) have been found in large numbers in north Alabama soybeans this year and some fields have already been sprayed twice. Numbers of 3CAH’s are comparable to the relatively high numbers observed in 2010. 3CAH girdling of seedling soybeans can result in plants falling over later when strong winds occur. Often plants that have been girdled and do not lodge produce normal yields. The current treatment threshold for soybeans less than 10 inches tall in Alabama is to treat when pests or damage is noted and stands are threatened. The Mississippi seedling soybean treatment recommendation for 3CAH is to apply insecticide from plant emergence to 10 inches in height when the plant stand is reduced below the recommended plant populations. Georgia’s soybean IPM guide recommends treating soybeans up to 12 inches tall when 10% of plants are infested with nymphs and/or adult 3CAH’s. The most common method for sampling soybeans for 3CAH is the sweepnet.  There is no research based threshold for seedling soybeans which states the number of 3CAH’s per sweep for a given row spacing that is needed to trigger an insecticide application. Reports indicate numbers of 3CAH’s per sweep are presently higher in drilled soybeans than in soybeans planted using a 30 inch or greater row spacing.  Soybean insecticide seed treatments to date have provided good control of 3CAH’s for approximately 3 to 4 weeks after planting but with the heavy pressure we are currently seeing even fields that have been planted with insecticide-treated seed should be monitored for damage. 3CAH damage tends to be greater in soybeans planted behind wheat than in full-season soybeans. Seedling soybeans sprayed with an insecticide frequently see 3CAH populations rebound within 2 weeks and another insecticide application may be required.

By: Tim Reed, Extension Entomologist, Auburn University